Method and system for dimpling metal sheets



Oct. l1, 1960 H. P. sHoEBRlDGE ErAL 2,956,148

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METHOD AND SYSTEM FOR DIMPLING METAL SHEETS Filed may 9, 195s 6 Sheets-Sheet 6 205 g l v\ J I 1 207 l 206 lesuuonl l 25o' 251 I uw QAnlLQELEAse T I 233 mi REMOTE CONTROL INVENTOR: #nemo Pamesa/06f Y GeoRef E. 565e United States Patent ffice 2,956,148 Patented Oct. l1, 1960 METHOD AND SYSTEM FOR DllVIPLlNG METAL SHEETS Harold P. Shoebridge, Gardena, and George E. Leger, Torrance, Calif., assignors to Aircraft Tools, Inc., Los Angeles, Calif., a corporation of California Filed May 9, 195s, ser. No. 734,276

17 Claims. (cl. 219-149) This invention relates to metal dimpling mechanisms, and more particularly to a novel method and apparatus for heating a metal sheet and applying pressure thereto to form a dimple.

Dimples are often formed in metal panels which are to be riveted together to form a unitary structure. Probably the most widespread use of dimpled panels is in the aircraft industry, where sheets of aluminum alloy have been used in building up the skin structure and interior walls of an aircraft. As is well known, such panels are dimpled so that the completed structure will be as strong as possible, e.g., so that plates forming the body and wings will withstand high shear forces.

The aluminum sheets to be dimpled are first apertured, as by drilling holes therein, at locations where they are to be riveted to another sheet.

After the holes are drilled, the aluminum sheet is placed between the dies of a dimpling machine. The dies, which have been previously heated to temperatures of about 650 F., are closed so as to touch the sheet around a hole therein. 'Ihe dies are held against the sheet for a time estimated to be that which brings the metal to the right temperature for dimpling, e.g., 300 F. for a typical aluminum alloy. At the end of this estimated dwell time for the dies, the dies are squeezed together to form a dimple on one side of the sheet. The sheet is then moved so as to position an adjacent hole between the dies, and the process is repeated.

One reason for heating the metal prior to forming a dimple is that if a dimple is formed when the metal is too cold, the dimple forming operation may result in minute fractures in the metal. Such fractures will enlarge where the sheet is subsequently subjected to high shear stresses, thus weakening the sheet and the entire structure of which it is a part.

If a dimple is formed when the metal is overheated, the metal will anneal during the dimple forming operation. Such annealing, of course, results in the dimple being too soft to aid a rivet in holding the sheet to an adjacent sheet in the presence of high shear stresses.

The time estimate for the conduction heating is arrived at by experimentation with a pilot sheet. Since aluminum is a good heat conductor, the heating of the metal around the first selected hole of the cold sheet causes the temperature around the adjacent hole to rise. Thus, the time needed to bring the metal around such adjacent hole up to dimpling temperature is necessarily less than for the first selected hole.

The time differential for heating the metal around that substantially the same time elapses between successive dimpling operations, (b) the holes are the same distance apart, and (c) the dies are maintained at a constant temperature. These factors are, of course, variable, and in actual practice the result may be that in the same sheet many of the dimples are formed with fractures, and many turn out to be annealed metal. In any event, the conventional method of dimpling results in a high rejection rate for aluminum alloy panels. Although such panels are relatively inexpensive, the time and labor loss as a result of such discards is a considerable factor in the overall cost of producing an aircraft.

As the speeds of modern aircraft extend to multiples of the speed of sound, the heating of the skin of an aircraft, due to friction, renders aluminum alloys unsafe for such structures. Accordingly, aircraft to be tiown at such high speeds must be made of materials having a much higher resistance to heating.

Titanium is a metal which has been found to withstand such high temperatures, and which is suited for building supersonic aircraft. As With those made of aluminum, sheets of titanium are dimpled for maximum strength against high shear stresses in the vicinity of rivets.

As is well known, titanium is an extremely expensive metal. in the assembly of an aircraft with panels of titanium, the rejection of only a few panels, due to improper dimpling, can add thousands of dollars to the cost of producing aircraft.

A much more serious problem arises where a supersonic aircraft is assembled with panels of titanium having faulty dimples which have gone undetected. Such panels constitute weak links in the structure. They may give way under the extremely high shear stresses created at supersonic speeds, and thereby result in loss of life and property.

It is an object of this invention to provide a novel method and system for dimpling metal sheets, in which the heating of the sheets to the proper temperature for dimpling is automatically determined.

It is another object of this invention to provide a method and system for dimpling metal sheets, in which the dimples can be formed at the proper temperature without experimentation.

Another object of this invention is to provide apparatus for forming a dimple in a metal sheet, in which the heating of the metal and the forming of the dimple are carried out automatically.

A further object of this invention is to provide an improved method and apparatus for dimpling metal sheets, which utilizes induction heating for heating the metal to the proper temperature for dimpling and in which respective means for heating the metal and forming the dimples are automatically synchronized.

Yet another object of this invention is to provide a mechanism for electrically controlling the heating of a metal sheet and forming a dimple therein,

Still a further object of this invention is to provide means for automatically determining when metal is at the proper temperature for dimpling, and for automatically forming a dimple therein at such temperature.

it is still another object of this invention to provide means for automatically heating a pair of dies used in dimpling metal sheets, and including means for keeping the temperature of the dies within a predetermined range.

A still further object of this invention is to provide, for a pair of dies used in dimpling metal sheets, means for preventing operation of the dies except when the sheet is in a predetermined position.

The above and other objects and advantages of this invention will become apparent from the following description, taken in conjunction with the accompanying drawings illustrating a preferred embodiment thereof, and in which:

Figure 1 is a side elevation view of an automatic machine for dimpling metal sheets, in which part of the machine housing is broken away to show the placement f certain controls, and in which respective induction heating units for heating the dies and a metal sheet to be dimpled are schematically illustrated;

Figure 2 is a front elevation view of the machine of Figure l, showing the location of means for measuring the temperature of the metal at an area to be dimpled, and showing front panel controls and visual indicators;

Figure 3 is a perspective view of the apparatus for heating a metal sheet, showing the arrangement of parts to effect movement of a heating coil toward and away from a position between the dies;

Figure 4 is a sectional view taken along the line 4-4 of Figure 3, further illustrating the cooperative relation of parts for controlling the position of the heating coil;

Figure 5 is an enlarged fragmentary view of the dies in position prior to forming a dimple, and showing the heating coil in position for heating a metal sheet located between the dies;

Figure 6 is a fragmentary View, similar to Figure 5, of the dies being squeezed together and forming a dimple in the sheet;

Figure 7a is a schematic diagram of a control circuit for preventing initiation of a dimpling cycle until the dies are at selected temperatures;

Figure 7b is a schematic diagram of a circuit for effecting sequential operations of valves in a pneumatic system used for moving the heating coil and squeezing the dies together to form a dimple;

Figure 8 is an enlarged fragmentary section view of the die heads, showing the arrangement of coil units for heating the dies, and of thermocouples used in detecting die temperature;

Figure 9 is a schematic diagram of temperature detection means used in conjunction with each thermocouple of Figure 8;

Figure 10 is a schematic diagram of a circuit for supplying current to the heating coil and for supplying operative voltage to the circuits of Figures 7a and 7b;

Figure 11 is a schematic diagram 'of the pneumatic diagram of the pneumatic system controlled by the circuit of Figure 7b;

Figure l2 is a schematic diagram of means to effect remote control of the machine of Figure 1 when the metal sheet being dimpled is of such size that the operator cannot reach needed controls on the machine;

Figure 13 is a partial section of the female die assembly, showing an alternative arrangement, employing a thermocouple for detecting the temperature of the metal sheet to be dimpled; and

Figure 14 is a sectional view taken along the line 14-14 of Figure 13, showing the end construction of the pilot rod used in forming the thermocouple.

Referring to Figures 1 and 2, the dimpling machine of this invention utilizes a conventional U-shaped housing 10, which is adapted, as indicated at 11 and 12, to rest on one leg 13 on a foundation. A female die assembly 14 is supported on the lower leg 13, and a male die assembly 15 is supported by the upper leg 16 of the housing 10 so as to be vertically aligned with the female die assembly 14. The male die assembly 15 is adapted for vertical movement toward and away from the female die assembly 14, and its position is controlled by a pneumatically operated tendem cylinder 17.

A metal sheet 18 to be dimpled is placed on the female die assembly 14, with an aperture therein disposed on the common axis of the dies. At this time, the dies have been heated to selected temperatures.

`The dies are adapted to be heated by conduction, and a control knob 20 on the front panel 21 of the housing 10 is an operation selector which is provided for controlling the heating of the dies. The position of the control knob 2t) determines whether one, or both, or neither of the dies will be heated.

For the purpose of heating the metal sheet 18 around the opening at which the dimple is to be formed, this invention provides a heating coil 22. The coil 22 is normally held in a retracted position. After the metal sheet 18 is inserted between the dies, and the hole therein at which a dimple is to be formed is properly positioned, a foot switch 23 is depressed to effect movement of the coil 22 forward and downwardly, so that the end loop 24 thereof rests on the metal sheet 18, as shown in phantom in Figure l.

When the coil loop 24 is in position against the metal sheet 18, current is supplied thereto from an induction machine 26, thereby to effect heating of the metal sheet 18 by induction.

A radiation pyrometer device 27 is used to detect the temperature of the metal in the vicinity of the opening in which the dimple is to formed. To this end, the pyrometer 27 is supported on the housing 10 above-the female die assembly 14. As indicated, the line of sight of the pyrometer 27 is directed to or focused at the center of the opening at which the dimple is to be formed.

When the temperature of the metal sheet 18 in the vicinity of the hole in which the dimple is to be formed is the correct dimpling temperature, the pyrometer 27 causes the coil 22 to be retracted. Upon retraction of the coil 27, the cylinder 17 is operated to cause the male die assembly 15 to be lowered against the sheet 18 t0 form the desired dimple.

Figures 5 and 6 illustrate the cooperation of the dies to form a dimple in the sheet 18. As shown, the female die head 28 has a central recess 29 in its upper end which is the female image of the desired form of dimple. The opening 30 in the sheet 18 is centered with respect to the recess 29 by means of a pilot rod 31 disposed within the die head 28. To aid in this centering operation, the pilot rod 31 is biased upward by a compression spring 32 disposed within the die head 28. Thus, when the sheet 18 is first placed on the die head 28, the rod 31 is depressed by the lower surface of the sheet 18. When the desired opening 30 is disposed above the center of the die head 28, the upper end of the pilot rod 31 is allowed to enter the opening and center it on the common axis of the dies.

The metal around the opening 30 is heated by the heating coil 22, as previously described. While the metal is thus being heated, `the male die head 33 is vertically spaced from loop end 24 of the coil 22, as shown in Figure 5. After the metal around the opening 30 reaches the proper dimpling temperature, the coil 22 is retracted, as previously explained, and the male die assembly 15 is lowered so that the die head 33 is forced against the metal sheet 18.

The dieI head 33 is provided with a tapered projection 34 which is the male version of the desired dimple. The tapered projection 34 terminates in a short cylindrical nose element or die pilot 35. When the male die assembly 15 is lowered, the male die pilot 35 enters the opening 30, forcing the pilot rod 31 down into the female die head 28. Movement of the male die head33 continues until the entire tapered projection 34 extends into the metal sheet 18. tIn this position of the diepheads 28, 33, the metal around the opening 30 on the under side of the sheet 18 is forced downward into the tapered recess 29 of the female die head. The metal thus forced into the recess 29 (see Figure 6) forms a dimple 36 of the desired configuration on the lower surface of the sheet 1S.

The details of construction of means for supporting and moving the heating coil 22 are shown most clearly in Figures 3 and 4, to which reference will be made along with Figure l. i v A The heating coil 22 and its operative structure are supported on a rectangular mounting plate 38 which is secured to the under side of the leg 16 behind the male die assembly 15. Secured to the lower surface of the mounting plate 38 are a pair of elongated, parallel, L- shaped members or rails 39, 40. The rails 39, 40 are adapted, as shown, to slidably support a plate 41.

The movable plate 41 constitutes a carriage for the heating coil 22. To this end, the plate 41 has secured upon its lower surface a U-shaped bracket 42, the open end of which faces the male die assembly .5. Extending between the legs of the bracket 42, and adjacent its forward end, is a rotatable shaft 43. One end of the shaft 43 extends through the bracket 42 and has one end of a lever 44 aiixed thereto. Y

The lever 44 is adapted to be turned. so as to rotate the shaft 43. Such operation is effected by a cam follower element 45 afhxed to the opposite end of the lever 44. The cam follower 45 is adapted to ride on a cam surface which, as illustrated in Figures l and 3, forms the lower edge of a plate 46 which is secured to the mounting plate 38 adjacent one of the rails 40. The forward portion 46' of the cam surface is parallel to the mounting plate 38, and the rear portion 46 thereof is tapered downwardly and rearwardly.

The heating coil structure is movable with the lever 44. To accomplish this, a cup-shaped element 4S is secured to the shaft 43 intermediate the legs of the bracket 42. Threaded into the cup 48 is a knurled cylinder 49 to which the upper end of the heating coil structure is secured.

When the cam follower 45 is on the forward part of the parallel portion 46' of the cam surface, the coil 22 is in a lowermost position, as shown in Figure 3, and with the loop end 24 thereof (as illustrated in phantom in Figure l) on the common axis of the dies. When the cam follower 45 moves from the parallel portion 46 to the tapered portion 46 of the cam surface, the end of the lever 44 attached thereto rocks downwardly, thereby to rotate the shaft 43 and cause the coil 22 to be raised to an uppermost position (the position shown in solid lines in Figure l).

Air pressure is utilized to control the position of the heating coil 22. To this end, the rod 50 of a cylinder 51 is secured to the back of the bracket 42, so that upon longitudinal movement of the rod 50, the cam follower 45 will be made to follow the cam surface S6-46.

Forward movement of the rod 50 is effected by air pressure applied to the rear of the cylinder 51 through a connection 52 to a valve 53.

To effect movement of the piston rod 50 rearwardly, so that the cam follower 45 will ride on the tapered cam surface 47 for retracting the heating coil 22, air is introduced into the forward portion of the cylinder ft. However, instead of introducing full how air directly from the valve 53 into the front of the cylinder 51 for this operation, the full flow air from the valve 53 is fed to the front of the cylinder 51 through another valve 54.

The valve 54 is secured, as by a plate 55, to the mounting plate 3S. The actuating stem 56 for the valve 54 is disposed in the path of the bracket 42, and is positioned to be actuated thereby at the point in its rearward travel at which the follower 45 starts along the inclined cam surface 47. The outer end of the valve stem 56 is bifurcated, and a small roller 57 is rotatably mounted between the lingers of the stem 56 so that its lateral surface will be engaged by the bracket 42.

While the bracket 42 is forward of the valve stem 56,

full ow or high-pressure air from the valve 53 is introduced into the front of the cylinder 51. For this purpose, a connection 58 is made to the valve 54 from the Valve 53, and a separate connection 59 is made between the valve 54 and the front of the cylinder 51. The valve 54 is opened in the non-depressed position of the valve stem 56, to allow the full flow air from the valve 53 to pass through the valve 54 and into the front of the 6 cylinder 51, thereby to effect rapid rearward movement of the cylinder rod 50, and hence of the coil 22.

When the bracket 42. engages the roller 57 to depress the valve stem 56, the valve 54 is closed, so as to cut off the full-flow air to the front of the cylinder 51. The connection 59 includes a T-connector 60, to one arm of which oriiiced air from the valve 53 is applied, as indicated at 61. Such oriced air is at reduced flow, thereby to cause the last portion of the travel of the rod 50 to be relatively slow, whereby the coil 22 is moved smoothly from its lowermost to its uppermost position.

As previously explained, operation of the heater coil 22 is effected only after the die heads are up to the selected temperatures. With this invention, there can be no doubt at this point, because movement of the coil 22 and of the tandem cylinder 17 are inhibited until such correct temperature conditions exist.

The arrangement for effecting heating of the dies, and detecting the temperatures thereof, is illustrated in Figure 8. The male die head 33 has secured thereto a small housing 65 which contains terminal leads 66, 67 for a heater coil 68 disposed within the head 33. The leads 66, 67 extend through the external cable 69 to be coupled to a source of current, all in a conventional manner.

Also disposed within the housing 65 is a thermocouple element which extends into the die head 33 so that the end thereof is adjacent the tapered die portion 34. The thermocouple leads 71, 72 connected to the element 70 extend through the external cable 69.

In a similar manner, a housing 74 secured to the lower die head 28 contains terminal leads 75, 76 to the ends of a heater coil 7'7 disposed within the die head 28. Also disposed within the housing 74 is a thermocouple element 78, the upper end of which is disposed adjacent the recess 29. The thermocouple leads 79, 80, together with the heater leads 75, 76, are led through an external cable 81.

Each of the thermocouples 70, 78 is utilized with a thermal relay device. Preferably, the thermal relay ernployed is the type of recording instrument described in the publication Weston Sensitive Relays, March 1954, published by the Weston Electrical Instrument Corporation, Newark 5, New Jersey. Such a relay, designated as TR1, is illustrated schematically in Figure 9 for use -with one of the thermocouple elements 70.

As shown in Figure 9, the thermal relay TR1 has a coil 82 connected at its ends to the thermocouple leads 71, 72. A pivotally mounted vane 83 is adapted to be moved under the influence of the eld of the coil 82. The outer Vend of the vane 83 carries a pair of contacts, TRlb and TRld, placed on opposite sides thereof. Two xed contacts TRla and TRc, which are small permanent magnets, are positioned so that when the vane is at one end of the' scale, the TRM, b contacts are in engagement, and when the vane is at the other end of the scale, the TRlc, d contacts are in engagement.

At the lower end of the scale, the contacts TRla, b are in engagement. Below the minimum temperature in a desired range from the die head 33, the contact TRla holds the contact TRlb thereto by magnetic attraction. For example, the desired range may be from 600 F. to 650 F. for a sheet of aluminum alloy to be dimpled. The vane 83 cannot move from this end of the scale until the temperature of the die head exceeds 600 F. Above this temperature, the magnetic field of the coil 82 is sutiiciently strong to cause the vane 83 to move to the right and separate the contacts TRla, IJ.

As the temperature of the die head 83 increases, the current through the coil 82 increases, whereby the stronger magnetic field causes the vane 83 to move further away from the contact T Rla, and in a direction of the fixed contact TRlc. When the die head 33 reaches the upper temperature in the range, the vane 83 is in a position wherein the permanent magnet contact TRlc attracts and holds the contact TRld in engagement therewith. As will be explained more fully hereinafter, current through 7 the heater coil 63 within the die head 33 will be removed if the temperature of the die head 33 increases above that at which the contacts TRlc, d come into engagement; in this manner, the temperature of the die head 33 is maintained within the desired range.

The circuit of this invention for controlling the heating of the dies and preventing other operations until the dies are at a selected temperature, is shown in Figure 7a. As previously explained, the position of the control knob 20 on the front panel of the housing 10 determines whether one, both, or neither of the dies will be heated. The control knob 20 is shown at the top of Figure 7a, and is adapted to rotate a shaft, indicated at 85, to which are iixed three spaced cam elements 86, 87 and 88. The cam elements are adapted to close respective switches 89, 90 and 91 in a predetermined sequence upon rotation of the control knob 20 from left to right. This sequence is as follows:

As indicated in Figure 7a, the far left position of the control knob 20 is an Off position, in which all of the switches are open. The first position of the control knob 20 to the right of the Off position causes the cams 36 and 87, by means of respective cam projections 92 and 93, to close the switches 89 and 90. In this position of the control knob 20, the end of the knob is aligned with the letter D on the panel 21, indicating dual-heater operation.

The next succeeding position of the control knob 20 to the right causes the cam projection 93 on the cam 87 to move to a position Where the switch 90 is opened. Although the projection 92 on the cam 86 is also moved, it is dimensoned to cause the switch 89 to remain closed. l'n this position of the control knob 20, indicated by S on the panel 21, to designate single-heater operation, only the upper die head 33 is conditioned for heating.

The succeeding position of the control knob 20 to the right of the S position causes the switch 89 to be opened and the switch 91 to be closed. A projection 95 on the cam 88 is at this point in position to close the switch 91. In this position, the control knob 20 is aligned with the letter C `on the panel 21 to designate dimpling with cold heaters.

Each of the switches 89, 90 and 91 is connected at one terminal, as indicated at 96, 97 and 98, to one terminal of an A.C. voltage source, as indicated at 99.

As shown at the top of Figure 7a, a lamp 100 is connected through the conductor 99, and through a conductor 101, across the output terminals of the voltage source, thereby to indicate that the machine is On. The lamp 100 is visible from the front of the machine, as shown in Figure 2.

Control of the heating of the upper die head 33 will first be explained, i.e., as `for single-heater operation.

The thermal relay TR1 has its vane 83 (and hence the contact TRM) connected at 102 to the switch 89. A control relay, R1, is connected between the fixed contact TRlc and the conductor 101. The vane 83 is illustrated schematically in its position in which its contact TRld is separated from its fixed Contact TRlc; yas previously explained, this is the condition of the thermal relay when the temperature of the upper die head 33 is below the maximum of the desired range.

The relay R1 has a pair of contacts Rla, b which connect the upper heater coil 68 between the conductors 101, 102. Thus, when the switch 89 is closed, the heater coil 68 is connected to the voltage source, thereby to start the heating of the upper die head 33.

Simultaneously, upon closing the switch 89, a second relay R2 is energized through the contacts TR1a, b. To accomplish this, the vane 83 (and hence the contact TR1b) is connected to the conductor 102, and the relay R2 is connected between the contact TRla and the conductor 101. Since the contacts TRla, b are closed when the upper heater coil `68 is initially energized, it will be seen that closing of the switch 89 connects the relay R2 across the voltage source.

The relay R2 has a pair of normally closed contacts RZa, b, through which another relay R3 is connected between the conductors 101 and 102. As soon as the switch 89 is closed to cause the relay R2 to be energized, the normally closed contacts R211, b are opened, thereby to prevent energization of the relay R3. As will be made more evident hereinafter, this operation prevents the Voltage source from being connected to a subsequent circuit for controlling the heating of the coil 22, and the operation of the dies, until the die head 33 is at the proper temperature.

When the temperature of the upper die head 33 moves above the minimum, the contacts TRla, b will open, because, as previously explained, the vane 83 will be moved away from the TRla contact. When this happens, the relay R2 is de-energized, thereby to permit the contacts R2a, b to be closed again.

Inasmuch as the fixed contact TRla is a permanent magnet, it can be expected to hold the TRlb contact in engagement therewith until the upper die head 33 has been heated to a temperature several degrees above the desired temperature, or until the magnetic eld of the coil 82 is strong enough to force the vane 83 away to separate the contacts TRla, b. This is undesirable, inasmuch as it is desired to start dimpling operations as soon as the temperature of the die head 33 enters the desired range. Accordingly, this invention employs means `for checking the die temperature by periodically deflecting the vane 83 so as to force separation of the .contacts TRla, b. As soon as the temperature of the upper die head 33 starts above the minimum temperature in the range, the next succeeding forcible separation of the contacts TRM, b will permit them to remain open.` Thereafter, continued heating of the die head 33 results in the vane 53 moving farther away from the TRla Contact, and toward the contact'TRlc.

The means for checking the temperature condition comprises a repeat cycle timer 104, which preferably is a constant speed motor, connected between the conductors 101, 102. Upon closing of the switch 89, the timer 104 is connected across the voltage source. Such connection of the timer to the voltage source causes its output shaft 105 to rotate at a constant speed. The shaft 105 `operates a cam element 106 which periodically closes a pair of normally opened switch contacts 107, 10S. The contact 107 is connected to the conductor 102, and a solenoid S1 is connected between the contact 108 and the conductor 101. Thus, the solenoid S1 is periodically connected to the voltage source through the contacts 107, 108.

When the solenoid S1 is energized, it actuates the vane 83 so as to separate the contacts TRla, b. How this is accomplished is shown in Figure 9 by the dotted connection 109 from the solenoid S1 to the vane 83. The solenoid S1 is arranged to deflect the vane 83 to the center of the scale, each time it is energized. For this purpose, the solenoid S1 is adapted to pull a slidable rod 110 through a fixed housing 111. The outer end of the rod 110 has a pair of elongated finger elements 112, 113 which are normally biased apart, as by a spring 114. When the rod 110 is attracted by the solenoid S1, it is withdrawn into the housing 1111, and the ends of the iingers 112, 113 are drawn together at the center of the scale. The vane 83 is in the paths of the fingers, so that -it is carried to the center of the scale as the fingers close together.

The shaft 105 of the timer 104 also operates a cam element 115 so as to periodically open a pair of normally closed switch contacts 116, 117. As shown, one of the contacts 116 is connected to the contact TRla of the thermal relay TR1, and the Contact 117 is connected to one contact R2d of the second of a pair of contacts, R20, d, controlled by the relay R2. The contacts R20, d are 9 open prior to closing of the switch 89. However, inasmuch as the relay R2 is energized immediately upon the switch 89 being closed, the relay R2 closes its contacts RZC, d. Thus, as soon as the relay R2 is` energized through the thermal TR1 upon closing the switch 89, the relay R2 is maintained in the energized condition through its own contacts R2c, d `and the switch contacts 116, 117.

After the upper die head 33 is up to temperature, andcontacts TRla, b are open, the next succeeding opening of the contacts 116, 117 by the cam element 115 breaks the connection between the relay R2 and the source, thereby causing the relay R2 to be de-energized. When the relay R2 is de-energized, the associated RZa, b contacts are closed and the contacts R2c, d are opened. At this point, for single-heater control, closing of the contacts R2a, b connects a relay R3 across the voltage source.

The relay R3 has a pair of normally open contacts R3a, b, connected across the switch 91 (see the lower left corner of Figure 7a). When the relay R3 is energized, these contacts, R3a, b, are closed. A lamp 118 connected between the switch 91, as at 119, and the conductor 101 is turned on when the contacts R3a, b are closed to indicate that the dimpling operations are ready to begin, ie., that voltage is available for the control circuits for operating the heating coil 22 and forming a dimple. The lamp 118 is Visible from the front of the housing 10, as shown in Figure 2.

The shaft 105 of the repeat cycle timer 104 preferably rotates rather slowly, eg., four cycles per minute. The cam element 106 is adapted to close the contacts 107, 108 twice during each revolution, and for this purpose is provided with a pair of projections 106', `as. shown. Thus, the contacts 107, 108 are closed every seven and one-half seconds. The louter edges of the projections 106 are preferably dimensioned to keep the contacts 107, 108 closed for a length of time suflicient to` permit the solenoid S1 to be energized, e.g., two seconds, so as to deflect the vane 83 and cause the contacts TRla, b to be separated.

A projection 115 on the cam element 115 is adapted to cause the contacts 116, 117 to be opened once during each revolution of the shaft 105. Further, the projections on the respective cam elements 106, 115 are located so that closing of the contacts 107, 108 occurs only when the contacts 116, 117 are closed, and opening of the contacts 116, 117 `occurs only when the contacts 107, 10S are open. The reason for this arrangement is to prevent application of Voltage to the circuit for controlling the coil 22, and the dimpling operations, before the upper die head is up to temperature. If the contacts 116, 33.17 were opened at the moment the contacts 107, 108 were closed, the ensuing separation of the contacts TRM, b by the solenoid S1 would break the connections between the relay R2 and the voltage source. This would cause the relay R3 to be energized to light the lamp 118 and provide voltage to be available for operating the coil 22 and forming a dimple, even though the die head 33 is not up to the proper temperature.

After the vane 83 of the thermal relay TR1 has begun t move toward the other end of the scale, the temperature of the die head 33 continues to increase, due to continued heating thereof. At the highest temperature in the selected range, the vane 83 is in a position where the contact TRld is attracted to the fixed Contact TRic. When the contacts TRlc, d come into engagement, the relay R1 is energized, thereby opening its associated contacts Rla, b, and thereby breaking the connection between the upper heater 68 `and the source. The die head 33 then begins to cool down.

The-periodic energization of the solenoid S1 causes the Vane 83 to be moved to the center of the scale. As soon as the die head 33 has cooled down sutliciently so that the contacts TRlc, d remain open, the relay R1 is again de-energized, thereby causing the contacts Rla, b

10 to close and permit the upper heater 68 to resume heating the die head 33. Thus the operation of the control circuit of this invention functions to keep the die head 33 heated to a temperature just below the upper end of the desired range.

For dual-heater operation, the above-described operations are carried out simultaneously for heating the lower die head 28. Another thermal relay, TR2, is utilized in connection with the thermocouple 78 (see Figure 7a) with associated contacts TRZa, b, c, d, arranged as in -the case of the thermal relay TR1. In a similar manner, a relay R4 is connected between the contact TRZc and the conductor 101, and the vane is connected to the switch 90, as at 121. The relay R4 has a pair of normally closed contacts R4a, b which connect the lower heater 77 across the voltage source when the switch 90 is closed to start heating the lower die head 28.

As with the thermal relay TR1, the contacts TRZa, b are in engagement when the lower die head 28 is cold. The vane 120 is connected to the switch 90, and a relay R5 is connected between the contact TR2a and the conductor 10]., to be energized immediately upon closing of the switch 90. The relay R5 has `a pair of normally closed contacts RSU, b connected between the contacts R251, b and the relay R3. When the relay R5 is energized, the contacts R5a, b are opened, to prevent energization of the relay R3 until both dies are up to the proper temperature. Thus, the relay R2 functions to keep the contacts R2a, b open until the upper die head 33 is at the proper temperature, `and the relay R5 functions to keep its contacts RSa, b open until the lower die head 28 is up to the proper temperature.

Manifestly, the system of this invention permits the die heads 28, 33 to be maintained at diierent temperatures, if desired.

The relay R5 has a second pair of contacts R56, d, which are clo'sed when the relay R5 is energized, and which provide a direct connection from. the relay R5 through a pair of normally closed contacts 122, 123 to the conductor 121. The contacts 122, 123 are similar to the normally closed contacts 116, 117 previously described, and are periodically opened, as by a projection 124', a cam element 124, which is driven by the shaft 109 of the repeat cycle timer 104. The cam element 124 performs .the same function for the contacts 122,

as does the cam element for the contacts 116, Similar y, the cam element 124 operates in conjunction with the cam element 106 to effect periodic checking of the temperature condition of the lower die head The means for periodically actuating the vane 120 so as to separate the contacts TRZrz, b is a solenoid S2 connected in parallel with solenoid S1. Thus, it will be seen that upon each closing of the contacts 107, 10S, both the solenoids, S1 and S2, are energized to actuate the respective vanes 83 and 120i.

As in the case of the upper die, opening of the contacts 122, 123 at a time when the contacts TR2a, b are opened, i.e., after the lower die head 28 has been heated slightly above its minimum temperature, results in the relay R5 being fle-energized to allow the contacts RSa, b to be closed. As previously explained, when the contacts R2c, b and R5a, b are closed, the die heads 28 and 33 are up to the desired temperatures. The relay R3 is thus energized to close thecontacts R3a, b, thereby lighting the lamp 118, and making voltage available for the subsequent controls for the dimpling cycle.

When the lo'wer die head 28 reaches the maximum temperature in the selected range, the vane 120 is in a position where contacts TRZC, d are closed thereby to energize the relay R4 `and open its contacts R451, b and disconnect the lower heater coil 77 from the source. Subsequent cooling of the lower die head 28 to the point where the vane 120 is in a position to keep the contacts TR2c, d separated, causes the relay R4 to again be energized, thereby closing the contacts R4a, b to re- "11 establish the heating current through the lower heater coil 77.

It will lbe noted that a capacitor 127 .and a resistor 128 are connected in series between the vane 83 and the fixed contact TRlc. This is a conventional .arc suppression network which operates upon separation of the contacts Tllc, d to extinguish or minimize an arc existing therebetween. A similar arc suppression network comprising a resistor 129 and `a capacitor 136 is connected between the vane 120 and the iixed Contact T 2c.

This invention utilizes means to establish a scale range for the respective vanes 83 and 120 to correspond to the temperature of the dies for the particular metal to be heated. As illustrated in Figure 7a, a pair of adjustable resistors 131 and 132 are connected in series with the thermo'couple leads 71, 72 and the coil 83 of the thermal relay TR1. Further, one of the resistors 132 is shunted by `a switch 133. For a particular setting of the resistors 131, 132, the switch 133 in the closed position reduces the total resistance in circuit with the thermocouple and the coil 812. Accordingly, the relay TR1 is adapted for operation in two temperature ranges. The lower range (the 'closed po'sition of the switch 133) may be for use with an aluminum alloy, eg., 600-650 F. The upper range (the open position of the switch 133) may be for use in dimpling titanium, e.g., 90W-950 F. The particular range corresponds to the setting of the resistors.

1n a similar manner, the thermocouple 78 has its leads 79, 80, and the coil 134 for operating its vane 129, connected in series with adjustable resistors 135, 136. One resistor 136 is shunted by a switch 137. The functions of the switch 137 and the resistors 135, 136 are the same as for the switch 133 and the resistors 131, 132,.

As illustrated at 138, the switches are ganged to facilitate placing them simultaneously in either the open or the closed position.

if it is desired to form a dimple with unheated dies, the control knob is placed in the C position, at which the projection 95 on the cam element 8S closes the switch 91. As will be apparent from inspection of Figure 7a, closing of the switch 91 immediately connects the lamp 1.18 to the voltage supply conductors 99, 101, and makes voltage available for the remainder of the control circuit of Figure 7b.

Prior to describing the control circuit of Figure 7b, the pneumatic circuit and associated apparatus for manipulating the heating ooil 22, and for effecting movement of the upper die head 33 to form a dimple, will be explained. y

The pneumatic circuit is illustrated in Figure ll, to which reference will be made along with Figures l to 6. The upper die head 33 (see Figure l) is secured to the lower end of a ram 140 which extends through the upper leg `16 of the housing `10. Within the leg 16, the ram 14@ has a reduced diameter section 141 which is surrounded by a cylindrical guide housing 142. The upper end of the ram 140 is an enlarged diameter section 143 extending above the guide 142. The ram 140 is biased upwardly by a compression spring 144 which surro'unds the reduced diameter section 141 within the guide Movement of the ram 140 is effected by the cylinder rod `146 of the tandem cylinder '17. The outer end of the cylinder rod 146 carries a roller 147, the periphery of which is normally positioned adjacent the upper edge of a cam lever `148, and adjacent the pivot 149 of the lever 14S. The lever 148 is pivoted on a plate 15d which extends downwardly from a supporting platform 151 tixed within the housing 10 above the roller 147.

When air is supplied to the cylinder to force the rod 146 forward, the roller 147 moves forward onto the upper edge of the lever 148. The lever 144 is in abutment with its lower edge, and `adjacent its movable end, with the ram 140. Forward movement of the :roller 147 thus causes the lever to' earn the ram downwardly.

At the end of the forward stroke of the cylinder rod 146, the male die pilot 35 extends into the opening in the material and (see Figure 6) the ram is forced downwardly to cause the dimple to be formed.

The ram is normally held at about the midposition of its total possible stroke. This is done so that only a short stroke thereof is required to close the male die head 33 upon the sheet 18. For this purpose, a cylinder 153, supported on the platform 151, has the end of its rod 154 disposed against the upper edge of the lever 148 opposite the ram 140. The rod 154 is adapted to be actuated by air introduced into the rear of the cylinder 153, as at 155.

The rod 154 is biased upwardly by a compression spring 156 (see Figure 1l). Air is introduced into the cylinder 153 under suicient pressure to hold the rod 154, and hence the ram 140, forced down to the desired short-stroke position above the metal sheet. This position depends upon the combined eiects of the compression spring 144, the compression spring 156, and the air introduced into the cylinder 153.

As shown in Figure 1l, the source of air pressure cornprises a conventional compressor 157, an accumulator 158, a iilter 159, and an oiler 160. For controlling the air into the cylinder 1'53, connections 161 and 162 from the source are made respectively to a regulator valve 163 and to the high pressure inlet port 164 of a control valve 165. The outlet port 166 of the valve 165 is connected to the rear of the cylinder 153, as indicated at 167. A pressure switch 16S is coupled to the line 165 to eiect predetermined functions, hereinafter to be eX- plained, When the pressure in the line 167 rises or falls about a predetermined value. The outlet of the regulator valve 163 is connected, as at 169, to the high pressure input 170 of a valve 171 which has its outlet port 172 connected to the exhaust 173 of the valve 165.

The valves 165 and 171 are adapted to be actuated by respective solenoids S3 and S4. Prior to energization of the solenoids S3 and S4, the valves 163, 165, and 171 are arranged, as indicated by conventional symbols, so that regulated air is applied to the rear of the cylinder. 1'53. The regulated air pressure determines the shortstroke position of the ram 140.

An outlet connection 174 from the source of air pressure is made to the high pressure inlet port 17S of the valve 53 which controls the cylinder 51 and the cylinder rod 50. As shown, the valve 53 has two outlet ports 177, 178 coupled respectively to the valve 54 and to the cylinder 51. The valve 53 is normally conditioned so that oriced air only is applied, as indicated at 180, to the front portion of the cylinder 51. The rod 50 is thus maintained in its rearmost position wherein the bracket 42 is in engagement with the roller 57, which, as previously explained, cuts otf air flow through the valve 54 and keeps the heater coil 22 retracted.

The valve 53 is adapted to be actuated by a solenoid S5. When the solenoid S5 is energized, the valve 53 is activated to introduce air into the rear of the cylinder 51 lto move its rod 50, and hence, the coil support bracket 42, forwardly to allow the heating coil 22 to be placed in position for heating the metal to be dimpled. Subsequent de-energization of the solenoid S5 causes the valve 53 to be de-activated, thereby to cause full ow air and oriced air to be introduced into the front of the cylinder 51 through the valve 54, and the oriiice 180. The rod '50 then begins to return to its original position, returning the bracket 42 with it. As previously explained in connection with Figures 3 and 4, the bracket 42 closes the Valve 54 on the return stroke of the rod 50, whereupon only oriced air at 180 is introduced into the front of the cylinder 51, thus causing the coil 22 to be lifted smoothly.

1n the system of this invention, the solenoids S3 and S4 are energized simultaneously upon de-energization of the solenoid S5. This causes the valve 165 and 171 to be activated, thereby to introduce f-ull line pressure and orificed air through the valve 165 into the rear of the cylinder 153. This operation causes the piston 154 to move down against the lever 148 and move the ram 140 down until the male die pilot 35 enters the opening 30 in the material. The'system at this point is conditioned to effect final movement of the ram 140 to form the desired dimple.

Movement of the cylinder rod 146 and its roller 147 is controlled through a set of valves 185, 186 and 187', adapted .to be actuated by respective solenoids S6, S7 and S8. The rear of the front portion 17 of the tandem cylinder 17 is connected, as at 188, to the outlet port 189 of the valve 186, the inlet port 190 of which is connected, as at 191 and 192, to the source of air pressure. The valve 185 has two outlet ports 193, 194 which are connected, as at 195 and 196, to the front and rear portions, respectively, of the rear portion 17 of the tandem cylinder 17.

The inlet port 197 of the valve 18'5` is connected, as at 198 and 199, to the outlet port 200i of the valve 187. This valve has its inlet port 201 coupled to the source of air pressure, as indicated at 202 and 203.

In addition, the inlet connection 198 to the valve 185 is coupled, as indicated at 204, to the outlet port 205 of a regulator valve 206. The inlet port 207 of the regulator valve 206 is coupled to the air pressure source.

In the de-cnergized conditions of the solenoids S6, S7 and S8, a full line air pressure is introduced into the front of the rear portion 17" of the tandem cylinder 17 so as to keep the rod 146 in its rearmost position, at which the roller 147 is adjacent the pivot 149 of the cam lever 148. ing in the sheet 18 to be dimpled, the solenoids S6 and S8 are energized to activate the valves 185 and 187, whereupon regulated air through the regulator valve 206 is introduced into the rear portion 17 of the tandem cylinders 17. Simultaneously, the front of the rear portion 17l is connected to exhaust through the valve 185, whereupon the rod 146 is caused to move forward.

At a predetermined point in the travel of the rod 146, when the male die pilot 35 has entered an opening in the sheet to be dimpled, the solenoid S7 is energized to activate the valve 186 so as to introduce full line air pressure into the rear of the forward portion 17' of the tandem cylinder 17. Thereupon, the roller 147 forces the cam lever 148 against the ram 140 so as to bring the die head 33 downward with sufficient force to form the dimple in the material. After the dimple is formed, the solenoids S3, S6, S7 and S8 are de-energized, thus deactivating the valves 165, 185, 186 and 187.

De-activation of the valves 185, 186 and 187 causes full line air pressure to be introduced into the front of the rear portion 17" of the tandem cylinder 17, so as to force the cylinder rod 146 rearwardly. De-activation of the valve 165 exhausts the cylinder 153, and the rod 154 is moved to its uppermost position by the spring 156. Thus, the ram 140 moves to its uppermost position, whereby the die head 33 is removed rapidly from the material. Thereafter, the solenoid S4 is de-energized and the valve 171 is deactivated to cause regulated air pressure, through the regulator valve 163, to be supplied to the cylinder 153, so that the cylinder rod 154 acts through the cam lever 148 to return the ram 140 to the short-stroke position.v

It is important that the return of the ram 140 to its short-stroke position always be made from the same position. If it were attempted to stop the ram in this position immediately upon leaving the metal sheet, i.e., to reduce air pressure until the rarn 140 was in the shortstroke position, friction in the pneumatic system would prevent the ram being returned consistently to the same position. Accordingly, in accordance with this invention, the starting point from which to return the ram to the short-stroke `position is always at the top of its full When the male die pilot 35 enters the open- 14 stroke, i.e., at the position where the air in the cylinder 153 is exhausted.

Synchronization of the numerous operations above described is accomplished through control relays and a plurality of switches which are actuated in a predetermined sequence. The control circuit incorporating these switches and relays is shown in Figure 7b. This control circuit will now be described, and reference will be made to Figures 1-6 and 8-11 to explain the location of various parts and their cooperative relation.

As shown, five relays R6, R7, R8, R9, R10 are employed in the control network of Figure 7b. The relay R6 has two pairs of contacts R6a, b and R60, d. The relay R7 has two sets of contacts R7a, b and R7c, d. The relay R8 has three sets of contacts, RSa, b, R8C, d and R8e, f, and the relay R9 has three sets of contacts, R9a, b, R90, d and R9e, f.

The relay R10 has two sets of contacts which are connected between a power source 210 (see Figure 10) and the induction machine 26 (Figure l) for heating the coil 22. Prior to the start of a dimpling cycle, and, as shown in Figure 10, the two pairs of contacts, R10a, b and R100, d, are in an open position. Also shown in Figure 1t) is a transformer 211 having its primary winding 212 connected across the power source 210. The contacts R10a, c are connected to the terminals of the primary winding 212. The secondary winding 213 of the transformer 211 constitutes the voltage source for the control circuit of Figure 7a. The power source 210 is a high voltage source for operating a conventional induction machine, e.g., 230 volts, A.C. at 60 cycles per second. The transformer 211 is a step-down transformer, effective to apply 11S-volts across the secondary winding 213.

Referring again to Figure 7b, the foot switch 23 is connected between the conductor 119 and through the contacts R7tz, b to a mode selector switch 215. As shown schematically, and as seen on the front of the machine in Figure 2, the selector switch 215 is adapted to be placed in one of two positions, H and N; the letter H indicates that the heater coil 22 is used in the dimpling cycle, and the letter N indicates that the coil 22 is not used.

In the H position of the switch 215, the closing of the foot switch 23 causes the solenoid S5 to be connected across the voltage source. To this end, the con tacts R911, b, which are normally closed, are connected between the selector switch 215 and the solenoid S5. As previously explained, energization of the solenoid S5 causes the valve 53 to be activated for moving the coil 22 forward and down to a position where it can heat the metal sheet 18.

When the end 4loop 24 of the coil 22 is in position for heating the metal, the carriage plate 41 (see Figure 3) actuates a switch 216 which is secured to the lower surface of the mounting plate 38. The switch 216 is connected between the H contact of the switch 215 and the relay R10, thereby to cause the relay R10 to` be energized. The contacts R10a, b and R10c, d (see Figure 10) are closed when the relay R10 is energized, thereby to connect coil 22 to the induction machine 26 to start heating the metal sheet 18.

The radiation pyrometer 25 has a built-in switch 217 (see Figure 7b) which is normally open. When the metal is at the proper temperature for dimpling (c g., 300 F. for aluminum, l000 F. for titanium), the switch 217 closes automatically. A radiation pyrometer of this type is described in the publication Rayotube Temperature Detectors, Assemblies and Accessories, published by Leeds & Northrup Company, 1955.

The switch 217 is connected between the relay R9 and the conductor 119, thereby connecting the relay R9 to the voltage source and causing it to be energized. This causes the normally closed contacts R9a, b to be opened, thereby to de-energize the solenoid S5 and de-activate the associated valve 53 to cause the coil 22 to be moved back from between the dies and raised to its uppermost position.

Simultaneously, the normally open contacts R90, d and R9e, f are closed. Closure of the contacts R9e, j causes the solenoid S3 to be connected across the voltage source. For this purpose, the path traces from the conductor 181 through the solenoid S3, the contacts R6a, b (which are normally closed), a pair of `contacts 218, 219 of a preheat switch 220 (the purpose of which will be described hereinafter), the contacts R9e, f and R7a, b, and the foot switch 23.

The relay R8 is connected across the solenoid S3, through its contacts R8e, f, and is thus energized simultaneously with the solenoid S3. Accordingly, the normally open relay contacts RSa, b and R8C, d are closed. Closure of the contacts R80, b connects the solenoid S4 across the voltage source, thereby to energize the solenoid S4 and activ-ate its associated valve 171. As previously explained, simultaneous activation of the valves 165 and 171 operates through the cylinder 153 to cause the ram 140 to be lowered until the male die pilot 35 enters the opening where a dimple is to be formed.

The previously described movement of the ram 148 to insert the male die pilot 35 in the opening 38 in the metal sheet 18 a-sstuned Ithat the opening 3@ was in the proper position to receive the male die pilot 35. However, it occasionally happens that an opening is not properly aligned between the dies when the male die is lowered onto the sheet. If the male die pilot 35 were allowed to come down under :such circumstances, it may be caused to bear against the metal sheet 18 with sulicient force to damage both the metal and the die.

In accordance with this invention, such an occurrence is obviated by a no-punch control positioned within the Ileg 16 of the housing 10 (see Figure 1) and adapted to be activated by the cam lever 148 when it starts down under the influence `of air pressure in the cylinder 153. As shown in Figure l, a switch housing 221 is pivotally mounted, as at 222, on the leg 16 of the housing 10. An adjustment screw 223 is `accessible from the front panel 21, for adjusting Ithe position of the switch housing 221. A ypin 224 for opening and closing the switch is adapted to be activated by a lever 225 which is pivotal-ly mounted, as at 226, to `the switch housing 221, and is provided at its lower end with -a roller 227.

The switch housing 221 is so positioned that the outer end of the cam lever will engage the roller 227 when the male die pilot barely extends into the opening in the sheet 18. If the male die pilot does not enter the opening, ie., if the opening is not properly aligned on the common axis of the dies, the outer end of the cam lever 148 will not have engaged the roller 227, It" the outer end of the cam lever 148 does not engage the roller 227, the solenoids S6, S7 and S8 cannot be energized to activate their respective lassociated valves 185, 186 and 187. Therefore, the `cylinder rod 148 cannot move, and the ram 140 will not form a d-imple.

However, if the male die pilot 35 does enter the opening in the metal sheet, i.e., the opening is aligned with the die pilot, the outer end or" the cam lever 148 does engage the roller 227 to lactuate the switch 225. As shown in Figure 7b, closure of the switch 225 will, inasmuch as the contacts R90, d are closed, permit voltage to be applied to portions of the circuit connected to the switch 225.

A lamp 229, which is visible from the front of the machine, is connected between the conductor 181 and the switch 225, as at 23th. When the switch 225 is closed, the lamp 229 is turned on and lindicates that voltage is available for operating the ram 140 to form a dimple.

Simultaneously upon the closing of the switch 225, the solenoids S6 and S8 `are energized, thereby to activate their associated valves 185 and 187 and start the cylinder rod 146 forward.

' The rod 146 carries an arm 231 (see Figures l and 7b) which, immediately upon forward movement of the piston rod 146, actuates a switch 232 mounted on the platform 151. As shown in Figure 7b, the switch 232 when actuated connects a timer device, labeled a dwell timer 233, between the conductors 101, 230. The dwell timer 233 has an associated pair of normally open contacts 234, 235 which lare adapted upon being closed to connect the solenoid S7 across the voltage source. The dwell timer 233 has an output shaft 236 which `actulates a contact closure element 237 after a predetermined time to close the contacts 234, 235. When these contacts are closed, thereby to energize the solenoid S7, the valve 186 is activated to cause full line presure to be introduced into the rear of the forward portion 17 of the tandem cylinder 17. Thereupon, as previously explained, the cylinder rod 146 moves forward and the cam lever 148 cams the ram 148 downward with suicient force to form the dimple.

The dwell timer 233 can be set for any desired time before activating the valve 186 to form the dimple. However, when the radiation pyrometer 27 and the coil 22 are used in the dimpling cycle, i.e., when the switch 215 is in the H position, the timer 233 is set for zero time, in which case it causes the solenoid S7 to be energized immediately upon closure of the pre-travel switch 232.

At the end of the stroke of the cylinder rod `146, the arm 231 closes a switch 240 which, as illustrated in Figure 7b, causes the relay R7 to be connected through the foot switch 23 across the voltage source. The contacts R70, d shunt the end-of-stroke switch 240; these contacts are normally open, but are closed when the relay R7 is energized, so as to maintain such Arelay energized.

Simultaneously, the contacts R7a, b are opened, thereby to de-energize all relays and solenoids, except the solenoid S4 and the relay R8, and to release the foot switch 23. Consequently, and as previously explained, the cylinder 1153 is connected to exhaust through the valves 165, 17,1, to permit the cylinder rod 154, and hence the ram 140, to be raised to the uppermost position.

Exhaust of the air in the cylinder 153, of course, causes a pressure drop in the line 167, thereby causing the pressure switch 168 to be opened. Opening of the pressure switch 168 causes the relay R8 to be de-energized, thereby de-energizing the solenoid S3 to de-activate the valve 165. Regulated air is thus introduced into the rear of the cylinder 153, and causes the ram 140 to be returned to the short-stroke position, in the manner previously explained.

4It will be apparent that sheets of any metal may be dimpled by the above-described sequence of operations. For any particular metal, the thermal relays TR1, TR2 are calibrated so that die temperatures are in the desired range, and the radiation pyrometer 27 lis adjusted so that its switch 217 is closed when the dimpling temperature for the particular metal is reached.

In order to heat a metal without using the coil 22, the mode selector switch 215 is moved to the N position. The switches 133, 137 in circuit with the thermal relays TR1 and TR2, are closed, thereby to condition the relays so that their vanes 83, move over a lower temperature scale range corresponding to lower temperatures of the dies. The mode selector switch 215 may be operated, las indicated at 242, in synchronism with the switches 133, 137, for automatically closi-ng the switches 133, 137 when moving the switch 215 to the N position.

In the N position of the selector switch 215, after the dies are up to temperature, the sequence of events is as follows:

Closing the foot switch 23 causes the solenoid S3 to be energized through the path comprising the normally closedcontacts R7a, b, the selector switch 215, the normally closed contacts 218, 219 of the switch 220, and the normally closed contacts R6a, b. Simultaneously, since the contacts R8e, f are closed, relay R8 is energized. This causes the normally open contacts R8a, b to be closed, thereby to connect the solenoid S4 across .the volt- .age source .and cause yit to Vbe energized.

-The .simultaneous energization of the solenoids `S3 and S4-results in activation of the valves 165 and 171.to apply pressure to the rear of the cylinder 153 and Yforce its .piston 154, along with the .cam lever 148 and the .ram .1146, downwardly. This application of pressure to the .rear ofthe cylinder .153 results in .the .pressure vswitch 168 being closed, whereby the .relay R8 is :held in .the energized :condition through .the ,pressure .switch 168 and Athe contacts R8C, fd.

As yin the case .above .described for the situation where the temperature selector .switch was .in .the H position, the .opening .inthe metal sheet lmust be .properly .aligned with the .male die pilot 35 in .order to cause the fno- ,punch .control switch-22510 .be closed. lAt the instant of-closingtheswitch 225, the .lamp ,229 lights up, to .signifyxthat the dimple cycle 'is on. Simultaneously, the solenoids `S6 and lS8 are energized, to `activate -the Iassociated valves 185 Iand 187'so asto start-the-cylinder rrod A1146 forward.

.Forward movement yof the rod 146 Acauses ythegpre- .tra-vel `switch .232 .to -.be closed :to start the dwell timer .233. .At the lend of the selected dwell time, during which the dies heat the metal to the dimpling temperature, `the -.contacts,-.theclosure element 237closes'thecontacts 234, .i235rso as to energize the solenoid .S7., andactivate its associated valve V186 'to lform :the dimple.

At -this point, 'the end of :stroke switch .240 Vis `tripped so as vtoienergize -the relay 'R7, thus .causing `the contacts .R7/'air to fhe opened so 1as fto rde-energize the remaining ,relays `with the exception -of the relay R8, .and all solenoidsfbut the -solenoid S4.

-When the contacts R7a, b vare opened, the solenoid 'S3 .-'s de-energized, .thereby to :connect the frear kof fthe {cyl- -inder i153 to exhaust `so the 1am .'-140 fwill move zto :its up- `permost position. Decrease in zthe .pressure ein the line i167 causes the ,pressure I.switch 1168 fte-open, whereupon w'the relay .R8 iside-energized, Aas is 'the fsolenoidS4. 'Tire valve 165 is thus -cle-activated, 'whereupon regulated air is :introduced into the rrear :of the cylinder '153 to return .theram 140-to its short-'stroke position.

At the end of :a :dimpling rcycle, the lmetal sheet fis vmovedsoras to position fanotheriopening betweenthe dies. Since the ram 140 is in :the short-stroke position 'at vthis time, the male die pilot 35 may make `itditiictilt to move the sheet about. For example, there Vmay be a projection on the sheet which extends 4far -enough above its -upper surface ythat it would strike the vmale die pilot 3S when moving the sheet. Onesolution`wou`ldbelto move the sheet-so as to move theprojec'tion around the'die pilot .35. However, this is undesirable where '.the sheet is unduly heavy, or unduly large and unwieldy.

This invention provides means Efor raising -the ram 140 `toits'uppermost position between dimpling cycles, whenfever desired. I'For this purpose a ram-release switch .2250 .is .connected between the solenoid S4 iand the lconiductor 1'19. As shown in Figure 7b, the ram=release :switch 1250 is connected in parallel with the contacts R8a, lb. Theswitch A250 is aspringibiased'switch'which ris normally biasedin the open position shown in Figure 7b. The push'button 251 for the-switch 250 is located 1onthe machine (see-Figure 2) `for easy access Vbythe oplerator. Depressing the push button 251 closes the -switch 250, thereby energizingthe solenoid S4 to Vactivate :the `valve d71. As previously'explained, activating the valve 171 alone connects 'the `cylinder 153 to exhaust, whereupon the ram '1'40is-raise'dtothe top of its stroke.

The ram `140 is Ymaintained in vthis position as long as ithe push button '251 is depressed. The clearance between-'thedie heads 28, '33 is here enough Vto permitthe metal `sheet therebetween to 'be moved 'without danger rlth'ata projection on the upper surface'thereof will kstrike :the male die pilot 35. After Athe projection'has cleared 18 the dies, the push button 251 is released, thereby deenergizing the solenoid S4 to de-activate the valve 171. Thereupon, regulated airis introduced into the rear vof the cylinder '153, and the ram '140 is lowered to itsshort- .stroke position.

This invention also includes means for selectively heating the sheet with 'the dies. The switch 2210 is used for this pre-heating. The switch 220 has, in addition to the contacts 218, 21'9 previously mentioned, another .pair of contacts 255, v256 connected between the conductor 119 and the contact `R6a. The .switch 220 is of the springloaded, push button ty-pe, which has two spaced contact closure arms 257, f258 which are mechanically connected together, as ait 259. The arm 257 is accessible to the operator,"being available at the front panel ,21 (see Figure 2). The arms 257, 258 larenormally biased `so that, as shown in Figure 7b, `the .contacts 218, 219 `are closed, and the contacts 255, ,256 y.are opened.

The switch 220 is yused rfor ypre-heat -only in the N position of the mode selector switch 215. Depressing the arm V257 causes it .to close the contacts 255, 256, and causes .the arm 258 .to move to a position wherein the contacts 218, 219are opened.

Closing .the contacts 255, 256 causes the solenoid ,S3 to be connected `between the conductors 101, 119, there- `by energizing the solenoid S3 andthe relay R8 shunting it. Since-energization ofthe 'relay R8 .causes Vthe solenoid S4 to be energized, .the valves 165, 171 are activated to lower the ram 146-to .position `the male die -pilot 35 'in an opening 4in the sheet. The resulting heatingof the sheet continues as long as the push button arm -257 is depressed. Meanwhile, .the opening :of .the contacts 21S, 219 prevents .any .other voperations vfrom taking place.

Occasionally, ametal sheet yto be dimpled may beso large that the .operator .cannot .reach the push buttons '251, 25.7., .or the foot switch .23. This inventionprovides a remote control unit 260 (see Figure `l.) for initiating a dimpling cycle, releasing the ram, or preheating the .materiaL This .invention .provides a remote control ,unit [265 (seeFigure l) forcontrolling these functions, and is Aprovided with corresponding push buttons 23', '251' and 25.7. As shown yin .Figure .12, `each switch ;is-.c0nnected ,in ,parallel .with the corresponding switches of Figure 7b. Thus, .the remote ram-release switch 250 is vconnected between .the conductor 1-19 and the 'solenoid S4; the pre-heat switch 220 is connected between the conductor 119 and the Contact R64; the .switch y23 is connected between the coductor 119 and the contact R711.

As shown Vin Figure l, .the cable 69,1the connections 266 .from the .switch 216 and .the connections 267 from the remote control switch 265 are led 1to afjunction box 268, from which output connection at 269 are led to a .main control panel 270 at the rear of the machine. VAll relays are located at the maincontrol panel 270, as are the .solenoids for the terminal relays TR1 and TR2. The cable 81, .and .the .induction machine 26 are also connected to .the control panel 270, as indicated at '272 and 273,.respectively. As shown at 274, connections are made from :the voltage source (of Figure 10) to the vcontrol panel 27.0, .to condition the-circuits vof Figures 7o and 7b for-operation as previously described.

The valves and their associated solenoids, and the source of air pressure, are `disposed :in the upper .part .of the machine,.as yindicated gener-allyfat 275. For :the sake of implifyingthe tpresentation in the drawings, .the plumbing vconnections .used throughout lthesystem Ihave notbeenshown.

Although the .female-die assembly 14-.is shown to .be held on a vertical support member 276, it will be Arecognized that -such assembly may be supported on a horizontal .arm .disposed ,betweenthe legs 13, v16 of the housing 10. Such anarrangement would facilitate dimpling 'of other than at panels, A,e.g.,.a panel forming theedge .of a wing of an aircraft.

An alternative arrangement for detecting the temperature of the metal sheet to be dimpled is shown in Figures 13 and i4. This arrangement employs a thermocouple which forms an integral part of the female die pilot. The pilot rod 31 of Figure 5 is replaced with a rod 31' which is cylindrical at its lower end, and has a generally frusto-conical coniiguration at its upper end.

The main body 277 of the rod is of dielectric material. The main body 277 forms the lower cylindrical portion of the rod. At its upper end, the main body 277 has opposed sector-shaped portions removed and replaced with a pair of metallic segments 278, 279. The segments 27S, 279 are made of different metals, of the type commonly used in thermocouples, e.g., Alumel and Chromel, and are suitably secured to the body 277.

When the upper end of the pilot rod 31 enters the opening 30 in the metal sheet 18, the metallic segments 278, 279 are biased against the metal, as shown in Figure 13. The metal in the sheet 18 thus constitutes the thermocouple junction.

Conductive leads 280, 281 are connected to the respective segments 27S, 279, and are connected to the ends of a coil 282. The coil is adapted to close a normally open switch 217 when the current therethrough is sufciently great. If desired, amplifying means may be utilized to couple the leads to the coil.

The switch 217' is used like the switch 217 of Figure 7b. When the desired temperature of the metal sheet 18 at the hole 3G is reached, the coil 282 closes the switch 217', to energize the relay R9 and initiate the previously described operations.

While we have illustrated a preferred embodiment of our invention, various modifications will be apparent to those skilled in the art which fall within the spirit and scope of our invention. Therefore, we do not intend that our invention be limited except as defined by the appended claims.

We claim:

1. In combination with a pair of dies to be pressed against opposite sides of a metal sheet to form a dimple thereon, wherein one die is tiXed in position and the other is movable with respect thereto; means to heat the dies; means to detect the temperatures of the dies; means to heat the metal by induction at a point to be dimpled; means to move the movable die so as to squeeze said point of the metal sheet between the dies to form a dimple; and control means operable by the detection means, when the dies are at predetermined temperatures, to eiect operation of the induction heating means, and said control means being operable, when the metal at said point is at a predetermined temperature, to eiect operation of the die moving means so as to form a dimple at said point.

2. In a dimpling machine having a pair of cooperating dies for forming a dimple on a metal sheet, a control system comprising: means to heat the dies; means separate from the die heating means to heat the metal by induction at a point to be dimpled; respective means to detect the temperatures of the dies and the metal at said point; pneumatic means to operate the dies so fas to squeeze the metal sheet at said point to form. a dimple; and means to effect operation of said pneumatic means for forming a dimple when the metal at said point is at a predetermined temperature.

3. In combination with a pair of dies to be pressed against opposite sides of a metal sheet to form a dimple thereon, wherein one die is iXed in position and the other is movable with respect thereto; respective means to heat the dies and the metal sheet, said means for heating the metal sheet being operable to heat the sheet in the area where a dimple is to be formed; respective means for sensing the temperatures of the dies and the metal sheet; means coupled to the die-temperature sensing means for effecting operation of the induction heating means only when the dies are at a predetermined temperature; means to move the movable die so as to squeeze said point ofthe metal sheet between the dies to form a dimple; and means coupled to the ,metal-temperature sensing means for effecting operation of the die moving means only when the metal at said point is at a predetermined temperature.

4. In combination with a pair of dies to be pressed against opposite sides of a metal sheet to form a dimple thereon, wherein one die is iixed in position and the other is movable with respect thereto: means to heat the dies; means to detect the temperatures of the dies; induction heating means for heating the metal sheet at the area. to be dimpled, said induction heating means including a coil connected to a source of alternating current, said coil being movable and adapted to be placed in a position adjacent the metal in said area, said coil normally being held away from said position, and normally being disconnected from said source; means operable at a predetermined temperature of said dies to place said coil at said position and connect it to said source; means to eiect movement of said coil away from said position, and to disconnect said coil from said source, when the metal in said area reaches a predetermined temperature; and means for pressing the sheet between the dies to form a dimple in said area, upon removal of said coil from said position.

1 5. In a dimpling machine having a pair of cooperating dies for forming a dimple on a metal sheet, a control system comprising: means to heat the dies; means to detect the temperatures of the dies; induction heating means for heating the metal sheet at the area to be dimpled, said induction heating means including a coil connected to a source of alternating current, said coil being movable and adapted to be placed in a position adjacent the metal in said area, said coil normally being held away from said position, and normally being disconnected from said source; means operable at a predetermined temperature of said dies to place said coil at said position and connect it to said source; a radiation pyrometer detection device for detecting the temperature of the sheet at said area; means operable by said detection device at a predetermined temperature of the metal in said area, to cause said coil to be moved away from said position and disconnected from said source; and means for pressing the sheet between the dies to form a dimple in said area, upon removal of said coil from said position.

6. In combination with a pair of dies to be pressed against opposite sides of a metal sheet to form a dimple thereon, wherein one die is Xed in position and the other is movable with respect thereto: means to heat the dies; means to detect the temperatures of the dies; induction heating means for heating the metal sheet at the area to be dimpled, said induction heating means including a coil connected to a source of alternative current, said coil being movable and adapted to be placed in a position adjacent the metal in said area, said coil normally being held away from said position, and normally being disconnected from said source; means operable at a predetermined temperature of said dies to place said coil at said position and connect it to said source; a thermocouple device having a junction completed through the metal in said area, for detecting the temperature thereat; means operable by said detection device at a predetermined temperature of the metal in said area, to cause said coil to be moved away from said position and disconnected from said source; and means for pressing the sheet between the dies to form a dimple in said arca, upon removal of said coil from said position.

7. The method of dimpling a metal sheet, wherein a pair of dies are adapted to be pressed against the sheet on opposite sides to form a dimple therein, comprising the steps of: heating the dies; heating the sheet by induction, after the dies are at predetermined temperatures, in the vicinity of the point at which the dimple is to be formed; and pressing the dies against the sheet to form the dimple after the sheet in said vicinity has 21 been heated to a temperature at which a dimple can be formed without altering the character of the metal.

8. The method of dimpling a metal sheet with a pair of dies, wherein said sheet has a predetermined dimpling temperature, comprising the steps of:r heating the dies; separately heating the sheet, inthe area to be dimpled, to the `predeterminedtemperature; and pressing the dies against the sheet in said area-to form a dimple thereon.

9. The method of dimpling a metal sheet with a pair of dies, wherein said sheet has a predetermined dimpling temperature, comprising the steps of: heating the dies; separately heating the sheet, in the area to be dimpled, to a predetermined temperature, while maintaining the dies in the heated condition; and pressing the dies against the sheet in said area to form a dimple thereon.

10. In a machine having apparatus for forming metal sheets, means to control the forming operation of the apparatus comprising: means to selectively heat the forming apparatus; means to detect the temperature of the forming apparatus; means to selectively heat the metal sheet at the area to be formed; means operable by the detection means at a predetermined temperature of the forming apparatus to eifect heating of the sheet by the sheet heating means; and means operable at a predetermined temperature at said area of the sheet to operate the forming apparatus for forming the sheet.

1l. In combination with a pair of dies to be pressed against opposite sides of a metal sheet to form a dimple thereon, wherein one die is xed in position and the other is movable with respect thereto; means to heat the dies individually, said means being selectively operable to heat one, both, or neither of the dies; means to detect the temperates of the dies; induction heating means for heating the metal sheet at the area to be dimpled, said induction heating means including a coil connected to a source of alternating current, said coil being movable and adapted to be placed in a position adjacent the metal in said area, said coil normally being held away from said position, and normally being disconnected from said source; means operable at a predetermined temperature of said dies to place said coil at said position and connect it to said source; means to eect movement of said coil away from said position, and to disconnect said coil from said source, when the metal in said area reaches a predetermined temperature; and means for pressing the sheet between the dies to form a dimple in said area, upon removal of said coil from said position.

12. In a dimpling machine having a pair of cooperating dies for forming a ydimple on a metal sheet, a control system comprising: respective means to heat the dies and the metal sheet, said means for heating the metal sheet being operable to heat the sheet in the area where a dimple is to be formed; means to operate the dies to form the dimple after the sheet in said area has reached a predetermined temperature, said means including a ram member for moving one die relative to the other, said ram member having a retract position wherein the separation of the dies is greatest; means in said die-operating means for normally holding said ram member in a retract position short of said retract position, wherein only a short stroke of said ram member and the one die effects formation of a dimple.

13. In a dimpling machine having a pair of cooperating dies for forming a dimple on a metal sheet, a control system comprising: respective means to heat the dies and the metal sheet, said means for heating the metal sheet being operable to heat the sheet in the area where a dimple is t be formed; means to operate the dies to form the `dimple after the sheet in said area has reached a predetermined temperature, said means including a ram member for moving one die relative to the other, said ram member having a retract position wherein the separation of the dies is greatest; means in said die-operating means for normally holding said ram member in a retract position short of said retract position, wherein only 22 a short stroke of. said ram member and the one die effects formation of' a dimple; and means selectively operable upon said die-operating means to move said ram member to its retract position, said die-operating means automatically returning said ram member to the short stroke position upon release of the selectively operable mean-s.

14., In ,combination with a pair of dies to be pressed againstoppositesides of a metal sheet to form a dimple thereon, wherein one die is fixed in position and the other is movable with respect thereto; means to heat the dies; means to detect the temperatures of the dies; means to heat the metal by induction at a point to be dimpled; means to move the movable die so as to squeeze said point of the metal sheet between the dies to form a dimple; control means operable by the detection means, when the dies are `at predetermined temperatures, to etfect operation of the induction heating means, and said control means being operable, when the metal at said point is at a predetermined temperature, to effect operation of the die moving means so as to form a dimple at said point; and means to render said metal heating means inoperative when i-t is desired to heat the sheet by the dies alone.

l5. In combination with a pair of dies to be pressed against opposite sides of a metal sheet to form a dimple thereon, wherein one die is fixed in position and the other is movable with respect thereto; means to heat the dies; means to detect the temperatures of the dies; means to heat the metal by induction at a point to be dimpled; means to move the movable die so as to squeeze said point of the metal sheet between the dies to form a dimple; control means operable by the detection means, when the dies are at predetermined temperatures, to effect operation of the induction heating means, and said control means being operable, when the metal at said point is at a predetermined temperature, to effect operation of the die moving means so as to form a dimple at said point; means to render said metal heating means inoperative when it is desired to heat the sheet by the dies alone; and means operable upon the die moving means when said metal heating means is inoperative to bring both dies into contact with the sheet, whereby to heat the metal by conduction.

16. A system for operating a pair of dies for squeezing a metal sheet therebetween so as to form a dimple thereon, wherein the dies are adapted to be heated prior to the dimpling operation, and wherein the metal of the sheet has a characteristic dimpling temperature which is higher than that to which `the dies are capable of heating it by conduction, comprising: induction heating means operable in the position of the sheet between the dies to heat the sheet to the characteristic dimpling temperature in the area to be dimpled; and means operable at the dimpling temperature of the metal in such area to squeeze the sheet between the dies to form a dimple thereon.

17. In a metal forming machine having cooperating dies for forming a metal sheet disposed therebetween, wherein a sheet must be heated to a characteristic forming temperature in the area between the dies prior to the forming operation, wherein the dies are incapable of heating certain metals by conduction to the forming temperature thereof, but are capable of heating other metals by conduction to their forming temperature, a system for effecting forming by the dies of sheets of metal of both types comprising: means for heating the dies; means for separately heating a sheet of one of the certain metals to the forming temperature thereof when such sheet is disposed between the dies; means for preventing operation of said separate heating means when a sheet of one of the other metals is between the dies, to permit the dies alone to heat the metal by conduction to the forming temperature; and means operative at ythe forming temperature of either type of sheet to operate the dies and form the sheet therebetween.

(References on following page) 

